1. Field of the Invention
The present invention relates to a printing medium which shows excellent printability in printing using water-based inks, in particular, ink-jet printing, has good surface gloss and can provide images having a high optical density, and an ink-jet printing process and an image-forming process using this medium.
The present invention also relates to a printing medium which is suitable for use in forming printed images having not only excellent water fastness and moisture fastness, but also high optical density and resolution and excellent surface gloss, and an image-forming process using this medium.
2. Related Background Art
As printing media used in formation of images by an ink-jet recording system, there have heretofore been used printing paper as described in Japanese Patent Publication No. 3-26665, which comprises a paper substrate and a coating layer provided on the paper substrate and containing finely powdered silica and a water-soluble binder such as polyvinyl alcohol, and glossy paper as described in Japanese Patent Publication No. 5-36237, which comprises an opaque base material such as a synthetic paper web and a film formed on the base material comprising a water-soluble resin as a principal component. Besides, described in Japanese Patent Application Laid-Open No. 63-265680 is cast-coated paper for ink-jet printing, in which a coating layer composed principally of silica and a binder is formed by a casting process.
With the recent improvement in performance of ink-jet printing apparatus, such as speeding up of printing and multi-coloring of images, printing materials for ink-jet are also required to have higher and wider properties for the purpose of providing images which satisfy various properties such as resolution and optical density in a well-balanced relation. Examples of such properties may include the following properties:
(1) ink-absorbing capacity being great, and ink being quickly dried);
(2) providing dots high in optical density and clear in periphery;
(3) providing dots having a substantially round shape and a smooth periphery;
(4) causing no unevenness of color strength at a solid printed area and providing an image having an even color density;
(5) providing an image having definite boundaries without causing bleeding even if inks of different colors are applied in an adjoining relation; and
(6) providing an image having good water fastness, moisture fastness and light fastness, and hence being able to stably store the image thereon for a long period of time without deteriorating it.
Various investigations have also been carried out with a view toward forming an image having high resolution and optical density comparable to a silver salt photograph or the like. As a means for achieving the image quality comparable to the silver salt photograph, there is a method of further improving surface glossiness and optical density while retaining printability such as ink absorbency, the ability to fix a coloring material in ink, water fastness of the resulting image, and coloring ability in color printing.
However, the surface of the coated paper described in Japanese Patent Publication No. 3-26665 is mat and hence unfit for an application of which gloss is required. The glossy paper described in Japanese Patent Publication No. 5-36237 can provide an image having high gloss and optical density, but involves a problem that since an ink-receiving layer thereof is a film of a hydrophilic resin, drying and fixing of ink applied to the surface thereof are slow, and so a printed area after printing (after application of the ink) is sticky to the touch for a long period of time, resulting in hindrance to continuous printing. This glossy paper is slow in drying of ink and hence tends to cause migration of ink on the surface thereof, which offers a problem that unevenness of color strength may often occur at a solid printed area. There is further a problem that the resulting image has poor water fastness due to its structure.
On the other hand, the cast-coated paper for ink-jet printing described in Japanese Patent Application Laid-Open No. 63-265680 is good from the viewpoint of absorption and fixing of ink, but involves a problem that the resulting image is insufficient in fastness properties such as water fastness and moisture fastness, or in coloring.
U.S. Pat. No. 4,879,166 discloses a recording sheet having an ink-receiving layer composed of a lower layer containing spherical silica and an upper layer containing pseudoboehmite. Since this sheet is provided with a large amount of a coating layer with a view toward surely imparting sufficient ink absorbency to the ink-receiving layer, the ink-receiving layer becomes brittle and hence offers a problem that dusting occurs to a great extent. Such a sheet is also insufficient from the viewpoint of water fastness and moisture fastness of the resulting image.